Can I buy the sleeve for a thermostat phial (tube)?

YI have a Coolzone CZ51109 under counter fridge with a freezing compartment in the top. When I moved into the flat with the fridge already there, the thermostat phial (the thin metal tube was) not neatly attached and hooked onto the clip on the underside of the evaporator but was simply bunched up in the open in the back of the freezing compartment area. I thought I’d tidy it up a bit and re-route it where it should be but now as it’s directly in contact with the evaporator, I have to turn the thermostat knob to maximum to get the fridge temp down to about 5 degrees and I’d like the option to get it a little cooler eg 2 or 3 degrees.

I’ve seen (and read about) some fridges having plastic sleeves over the thermostat phial so I’d like to buy a length for this fridge and hopefully rectify this issue in one go. Is this stuff available seperately or will ordinary clear plastic tubing do the trick? Any idea how much of the phial would normally be covered in this way and where (if anywhere) the phial should make direct contact with the frosty evaporator?